1. Field of the Invention
This invention relates in general to magnetic flux sensing apparatus and, in particular, to a magnetic head of the type employing a thin magnetic film structure as a magneto-resistive element responsive to the flux being sensed.
2. Background Relative to the Prior Art
Playback of recorded signals from a magnetic recording medium by means of a conventional magnetic head that is sensitive to flux rate-of-change is difficult for low recorded signal frequencies, and theoretically impossible for recorded DC signals, or when there is no relative motion between the recording medium and the magnetic head. Accordingly, various techniques have been proposed for sensing magnetic flux, as opposed to the rate-of-change of such flux, e.g. Hall effect, flux gate, and magneto-resistive devices, thereby to permit recording media to be used as optimally as possible.
With regard to the matter of magneto-resistive devices for sensing magnetic fields, the use of a thin magnetic film for field sensing purposes is known. Representative prior art depicting the use of magneto-resistive thin-film structures can be found in the following references: U.S. Pat. No. 3,731,007; U.S. Pat. No. 3,947,889; U.S. Pat. No. 3,921,218; U.S. Pat. No. 3,945,038; U.S. Pat. No. 4,051,542; and U.S. Pat. No. 4,413,296. Typically, a thin (planar) magneto-resistive film is employed to sense a magnetic field to which it is exposed by passing an electrical sense current (either AC or DC) through the film, the film magnetization vector being canted with respect to the direction of current flow. The field being sensed exerts a torque on the magnetic moment of the film, causing the resistance of the film to increase or decrease depending on the sense and magnitude of the field. The resistance of the film is, therefore, the analog of the field strength.
There are, within the prior art, two general types of thin-film magneto-resistive heads: a first type in which a medium-contacting structure in a magnetic yoke (or similar element) carries recorded signal flux away from a magnetic recording medium and applies such flux to a thin-film magneto-resistive element disposed in a given region of the yoke (or similar element); and a second type in which an edge of a magneto-resistive element is adapted to ride along the surface of a magnetic recording medium to pick up magnetic signals recorded thereon. Compending U.S. patent application Ser. No. 644,894, U.S. Pat. No. 4,644,430, filed in the name of William French, is directed to the concept of slotting "yoke-connecting" portions of the magneto-resistive element of the first type magneto-resistive head, thereby to preclude the magnetic short circuiting of signal flux by the yoke. By contrast, published Japanese Application No. 56-198506 is directed to the idea of slotting that side of magneto-resistive element of the second type magneto-resistive head which is distal with respect to its medium contacting edge, thereby to force sense current into the flux sensing edge region of the magneto-resistive element. The invention, as will appear below, is applicable to both types of magneto-resistive heads.
Magneto-resistive elements employed in connection with magneto-resistive heads are characterized by a susceptibility to thermally generated noise. This is especially so in the case of the aforenoted second type of magneto-resistive head, since the signal sensing magneto-resistive element of such a head is adapted to ride, abradingly, in contact with the medium the recorded signals of which it is disposed to sense.